1. Field of the Invention
This invention relates to open cycle, ocean thermal energy conversion systems, and more particularly, to a steam flow control and bypass arrangement for regulating motive steam flow through a turbine component of the open cycle OTEC systems.
2. Description of the Prior Art
Ocean thermal energy conversion is a process by which the normal temperature difference existing between relatively warm surface waters and relatively cold, subsurface waters is utilized to develop a pressure difference across a turbine through which a motive fluid is expanded. The surface of large water bodies, such as oceans, acts as a large solar energy collector for heating the exposed water. The solar heated water is partially flashed into steam which acts as the cycle's motive fluid. The motive fluid's expansion through the turbine causes the turbine's rotor structure to rotate. A generator suitably coupled to the turbine's rotor rotates therewith and produces electrical energy. Due to the small temperature and pressure differences typically found in ocean thermal energy conversion cycles (30.degree. F. and 0.3 psi by example), the cycle efficiencies are rather low. Since no fuel is consumed, the cost of operation for an ocean thermal energy conversion system is substantially reduced over conventional cycles and the primary factor limiting their use is the capital and construction costs of the equipment components. Components such as the turbine and heat exchangers must, by necessity, be very large to yield reasonable net electrical power output.
Ocean thermal energy conversion systems are typically classified to be of the open and closed cycle variety in which seawater and other volatile fluids are respectively utilized for the motive fluid. While the cycle varieties each have certain advantages over the other, a primary disadvantage of the open cycle OTEC has been the extremely large floating platform or hull structures required to support the power generation equipment and the high cost for materials and construction thereof. Reduction in the size and cost of the large platform structures required for open cycle OTEC power systems could provide a favorable advantage for such open cycles when compared with closed cycle OTEC systems. Platform elimination and/or size reduction was disclosed in J. M. Wittig's commonly assigned patent application Ser. No. 934,575. Such platform elimination utilizes optimum relative equipment disposition and integrates the equipment casings and supporting platform into one structure of complex shape. Due to the functional integration of the equipment casings and supporting platform, the resulting complexly shaped structure lent itself to fabrication from prestressed concrete. A fast responding steam flow control device for installation therein was sought to prevent turbine-generator overspeed after full load dump. It was determined that the flashed steam must be diverted around the turbine to reduce its torque and acceleration to zero as well as maintain evaporator-condenser equilibrium. An annular vane structure for bypassing steam through an annulus between rotatable turbine blades and the turbine's casing as disclosed in B. L. LaCoste's copending patent application Ser. No. 918,127 was considered. Such annular vane structure's adaptation to J. M. Wittig's functionally integrated system structure was judged economically unfeasible. System vacuum reduction, as also disclosed in patent application Ser. No. 918,127, presented a disadvantage of exerting excessive pressure loads on the complexly shaped prestressed concrete system structure. Furthermore, the large steam volumetric flow rates typically encountered in open cycle OTEC systems render the use of conventional stop valves for Wittig's functionally integrated system structure impractical due to their excessive size, pressure drop, inertia, and response time.